Automatic telephone system



Jan 26, 1932. T. F. cRocKER AUTOMATIC TELEPHONE SYSTEM Filed May 6, 1927:5 Sheets-Sheet I'm/en Thomas FEI'UlZkEZ" Jan. 2%,, 1932.. T. F. CROCKERAUTOMATIC TELEPHONE SYSTEM Inuen UT" Thumaa PEP/Jake? Jan. 26, 1932.. T.F. cRocKER AUTOMATIC TELEPHONE SYSTEM Filed May 6, 1927 3 Sheets-Sheet 3Thczmas F. Eruukezr till Patented Jan. 26, l932 STATES THUMAES l2.CRUUKER, 01" CHICAGO, ILLINOIS, ASSIG-NOR, BY MESNE ASSIGNMENTS, Tessocmrnn ELECTRIC LABORATORIES, INC., OPE CHICAGO, ILLINOIS, ACORPORATION QT DELA'WARE AUTOMATIG TELEHONE SYSTEM Application filed May6, 1927. Serial No. 189,421..

This invention relates to telephone systems in general, but is moreparticularly concerned with small automatic telephone sy sterns commonlyknown as private automatlc exchange systems.

The object of this invention, broadly stated, is the provision. of newand improved circuit arrangements for an attendants cabinet and of newand improved automatic switch ing apparatus, which are particularlydesigned for use in private automatic exchange systems.

A particular feature of this inventlon is that by the momentaryoperation of a key individual to an incoming trunk from a mam automaticexchange to the private automatic exchange, the attendants telephoneequipment including her dial is automatically associated with thatparticular trunk, after which the attendant may dial over thatparticular trunk in either direction, the direction being determined bythe setting of a common dialing key. The necessity of having a dialingkey and associated controlling equip ment for each incoming trunk iseliminated.

Another feature of this invention is that by reason of the new andimproved circuit arrangements for the attendants cabinet, it has becomepractical to remove all the con trolling relays associated with theattendants cabinet from the cabinet, and mount them on frames at anyconvenient place remote from the cabinet. The cabinet itself need houseonly the necessary keys and supervisory lamps, making it relativelysmall and inexpensive.

Another feature of this invention is the provision of a new and improvedconnector selector repeater designed for giving so-called discriminatingservice controlled over a discriminating conductor. The connector may betaken into use either by a private automatic evcl'lange subscriber or bythe attendant. and when the connector is used by the attendant, thediscriminating conductor serves as a signalling conductor for operatinga supervisory sinnal at the attendants cabinet.

These features and other features pertaining to the circuits and to themanner inwhichconnections are established and supervised by theattendant, will be described in detail in the following specificationwith the aid of the accompanying drawings comprising Figs. 1, 2, and 3.These drawings illustrate by means of the usual schematic circuitdiagrams a private automatic exchange system and, to be most easilyunderstood, should be placed with Fig. 2' to the right of Fig. 1 andmoving in one direction only. The lineswitch other sumlar lineswltches,

LS, together with has access to the group of connector selectorrepeaters by way of trunk lines, one of which is shown comprisingconductors 5 to 8, inelusive, terminating in the connector selectorrepeater C. (Hereafter the connector selector repeater G will bereferred to as merely connector U.)

Mechanically the connector 0 is of the well known Strowger vertical androtary type, having horizontal rows or levels of bank contacts, whichare multipled with those of the other connectors of the group. In anumber of levels of the connectors access is had to the lines of theprivate automatic exchange subscribers, including the line of substationA aswell as the line of substation A. In one particular level in thebanks of the connectors access is had to one or more information trunksfor extending connections to the attendant. One of these trunks is showncomprising conductors 301, 302, and 303 accessii ticular private Iautomatic exchange subscribers are permitted service to the mainautomatic exchange or to the attendant, while the other privateautomatic exchange subscribers are restricted to local calls within theprivate automatic system. At the lineof the jumper 11', whereas at thelineswitches of the restricted subscribers, this jumper is omitted. Theconnector such as connector 0 either extends or prevents the extensionof a connection to one of the outgoing trunks or to the attendantdepending on whether or not ground potential is supplied to thediscrimmating conductor 6 from the lineswitch by which it is seized.These operations will be described more in detail later.

In Fig. 2 is shown the trunk relay group TRG for the outgoing trunk tothe main automatic exchange comprising conductors 202 and 204. At theprivate automatic exchange, this trunk has two branches. One branch aspreviously mentioned comprises conductors 202, 203. and 204 accessibleto the connectors over which calls to the main exchange are extended.The other branch comprises conductors 252, 253, and 254 terminating inthe lineswitch LS, Fig. 1, over which calls from the main exchange to aprivate automatic exchange subscriber are extended, the banks of thelineswitch LS being mnltipled with those of the other lineswitches. Thelineswitch LS may be of the same type as the lineswitch LS.

At the main automatic exchange the trunk comprising conductors 202 and204 terminates in the individual lineswitch LS and is accessible in thebanks of connectors such as connector C in the well known manner. Thelineswitch LS may also be of the same type as the lineswitch LS shown inFig. 1, though the wiper for the discriminating conductor isunnecessary, and further the ground conncction to the lower conductor atthe contacts of the switching relay is omitted. Thelineswitch LStogether with the other line switches of the trunks from the privateautomatic exchange, has access in its banks to incoming selectors one ofwhich is shown designated S The selector S as well as the connector Cmay likewise be of the Strowger vertical and rotary type well known inthe art. The automatic switches at the main exchange do not particularlyconcern the invention, and are therefore shown only in skeleton. Itshould also be noted that the invention is not limited to a mainautomatic telephone system. The main exchange might also be a manualexchange. In this latter case the trunk lines from theprivate automaticexchange would terminate in jacks in the well known manner.

Within the dotted rectangle in Fig. 3 is shown the attendants telephoneset TS and the various keys and lamps of the attendan'ts cabinet.Individual to each of the interexchange trunks are three lamps and atwowa key such as the lamps L L and L an the key K which are individualto the inter-change trunk shown in Fig. 2. For each information trunk(over which the unrestricted subscribers may call the attendant) thereis a lamp and a key such as the lamp L and key K of the informationtrunk comprising conductors 301, 302, and 303. Besides this equipmentthere is a common dialing key K This key is operated in one direction todial out over a trunk to the main automatic exchange, and in the otherdirection while operating the automatic switches in the privateautomatic exchange. The attendants cabinet is also provided with key KBy operating this key to the right, the buzzer B is connected, so thatit sounds on all incoming calls, as will be described more fully later.By operating the key to the left a connector switch in the privateautomatic exchange that has been operated may be released withoutdisturbing the rest of the connection.

The attendants telephone set TS is a regular desk telephone set of theautomatic type, except that additional switch hook springs 399 areprovided for controlling circuits to be described subsequently.

Inthe left half of Fig. 3 is shown a group of relays two of whicharecommon equipment while the relay 300 controls the connection of theinformation trunk comprising conductors 301, 302, and 303', with theattendants telephone set. The conductors 301', 302, and 303' representanother information trunk accessible in the banks of the connectors inthe same level as the trunk comprising conductors 301, 302, and 303. Theconnection of this trunk with the attendants telephone set is controlledby relay 300.

With this general description ofthe features of this invention and theapparatus involved in mind, a detailed description of the operation willnow be given. The operations involved in setting up a connection fromthe main automatic exchange to a subscriber in the private automaticexchange will first be described. For this purpose, then, it will beassumed thatconnection is desired with the subscriber at substation A bysome main automatic exchange subscriber and that a connection has beenextended to the private automatic exchange over the trunk comprisingconductors 202 and 204: by way of the connector C, for example. As soonas this trunk line is seized at the main automatic exchange, a ringinggenerator is intermittently connected to the trunk at the main automaticexchange and a direct current circuit is closed for relay 207 whichextends from ground through the ringing generator at the main exchangeor direct ground (depending on the particular time when connection isn-- And established) over conductor 204, contacts 214, through theresistance R through the winding of relay 207, contacts 21 overconductor 202, through the winding of the ring cutoff relay of theconductor C to battery. Relay 207 operates immediately and places groundpotential on the release conductor 203 at contacts 240, therebyimmediately guarding this trunk against seizure by a connector in theprivate automatic exchange. The resistance of relay 207 and Ris'sufiiciently high to limit this direct current flow to the extentthat the ring cut-off relay of conhector is not operated. Upon the firstapplication of ringing current to the trunk conductors, ringingcurrent-responsive relay 209 at the private automatic exchange operates,its circuit including the two trunk condoctors and contacts 214. Relay209, in operating, closes a circuit for signalling relay 208. Relay 208operates and closes a locking circuit for itself at contacts 244, thiscircuit including contacts 237 and 23-2; completes another groundconnection to release conductor 203 at contacts 241; and at contacts 243closes a circuit for the lamp L at the attendants cabinet in series withrelay 314, this circuit likewise including contacts 237 and 232. Lamp llights, which apprises the attendant of an incoming call over thisparticular trunk. When the attendant is absent from her desk or isattending other duties, she may lreep the key K operated to the right.in that case, the operation of relay 314 closes a circuit for the buzzerB which on sounding gives further evidence of the incoming call.

When the attendant is ready to answer the call, she removes her receiverfrom its switch hook if it has not been removed previously andmomentarily operates the key K to the left. The latter operation, withthe receiver removed, closes a circuit for the upper winding of relay204 which circuit includes the switch hook contacts 399, contacts 310,and contacts 315 of the key K. Relay 204 operates and performs thefollowing circuit changes:

At contacts 227 relay 204 closes a locking circuit for itself throughits lower winding which includes contacts 233, winding of relay 313, andswitclrhook contacts 399. Relay 313 operates over this circuit and byseparating contacts 310 opens the initial energizing circuit of relay204 and prevents the energizetion of any other relay similar to relay204 should the attendant inadvertently operate some other key similar tothe key K at this time.

At contacts 226 relay 204 closes a circuit for the upper winding ofrelay 206. Relay 206 operates and prepares a holding bridge at contacts239, and opens the initial locking circuit for relay 208 and also thecircuit of the lamp l1 and relay 314 at contacts 237.

Relay 208 is held operated, however, over the I holding circuit closedat contacts 225' by relay 204. The current flow through lamp L and relay314 is limited, however, by reason of the resistance R to the extentthat lamp L is extinguished and relay 314 is insufficiently energized tomaintain contacts 311 closed. As a result the lamp L is extinguished andthe circuit of buzzer B (if connected) opened. As a further resultof theenergiza-- tion of relay 204 which effects the closure of contacts 223and 228, andas a result of the closure of contacts 235 and 236 by relay206, the common conductors 351 and 352 are connected to the trunkconductors 252 and 254 terminating in the lineswitch LS, Fig. 1. Theconductors 351 and 352 are bridged by the operators telephone set andtherefore the lineswitch LS is caused to operate in the usual manner andselect an idle trunk accessible in its banks.

Another result of the operation of relay 204 is the placing of a bridge.across the outgoing trunk conductors 202 and 204 by the closure ofcontacts 222 and 230, this bridge including the retard coil 312, thecommon conductors 361 and 362, and relay 201. The re sistance of relay201 and of the retard coil 312 is comparatively low so that the currentflow over the outgoing trunk conductors is increased sufficiently tocause the ring cut-off relay in the connector C to operate and disconnect the ringing generator and itself from the trunk conductors andcomplete the tallc ing connection to the attendant. Relay 201 nowoperates from current received through the windings of the hack bridgerelay in the. connector C at the main automatic exchange and at contacts211 closes a circuit for relay 202. Relay 202 operates and completesanother ground connect-ion to release trunk conductor 203 at contacts212, opens the circuit of relay 207 and the resistance R at contacts214, and closes the circuitof lamp L at contacts 215, this circuitincluding switch hook springs 399. The lighted condition of lamp Lindicates the busy condition of this particular trunk. Relay 202, inoperating, also closes a circuit for relay 203 at contacts 213, thiscircuit including contacts 219, the lower trunk conductor 204, and thelower winding of the back bridge relay of the connector C Relay 203 inoperating closes a locking circuit for itself at contacts 218independent of the lower trunk conductor, and by separating contacts 217and closing contacts 216 a bridge which is to include relays 201 and 207and is later to be placed across the trunk conductors is prepared.

As previously stated, the line switch LS is caused to operate and selecta trunk accessible in its banks extending to an idle connector by reasonof the telephone set being bridged across the conductors 252 and 254. Itwill be assumed that the connector C is the one selected, and whenconnection is extended thereto, line relay 11 operates in the usualmanner and closes the circuit of the release relay 12. Release relay 12operates and prepares the impulsing circuit at contacts 28, and placesground potential on the release trunk conductor 7 at contacts 27. As aresult ground potential is also connected to the discriminatingconductor 6 by way of contacts 33 and contacts 34. This closes a circuitfor the supervisory lamp L at the. I attendants cabinet and also anotherholdlng circuit for relay 208, these circuits extending over conductor 6through the lineswltch LS", over conductor 253 to the lamp L and throughresistance R contacts 243 and 244 to relay 208. As a result the lamp Llights. Resistance R is now in parallel with resistance R but still thecurrent flow through lamp L is insufficient to cause the lamp to light;nor is the current through resistances R and R sufficient to operaterelay 314, though this relay may be operated since it operates onall'incoming calls.

All of the operations described after the attendant removed her receiverand momentarily operated the key K to the right have taken placeautomatically responsive thereto. The attendant is now in talkingconnection with the main automatic exchange, and asks the callingsubscriber the name or number of the party with whom he wishes to speak.After receiving this information the attendant operates the commondialing key K to the right and then dials the number of the i calledparty. Throwing the key K to the right merely opens the talking circuitfrom the attendants cabinet back to the main automatic exchange toprevent the calling subscriber at the main automatic exchange fromhearing clicks which would be produced by the operation of theattendants dial.

Responsive to the dialing of the first digit of the called number thevertical magnet 20 of the connector C is operated to step the switchwipers 65, 66, and 67 opposite the level of bank contacts in which theline of the substation A is accessible (having assumed that substation Ais the called substation). The series relay 13 operates in series withthe magnet 20, and being slow-acting maintains its armature attractedthroughout the vertical movement of the switch wipers. At the cessationof the impulses produced by dialing the first digit of the calledsubscriber, relay 13 deenergizes and prepares the circuit for the rotarymagnet at contacts 30.

Responsive to the dialing .of the. second digit of the called number,rotary magnet 21 operates and rotates the switch wipers into engagementwith the set of bank contacts ter-' minating the called line. Relay 18operates in parallel with magnet 21, and being slowacting maintains itsarmature attracted throughout the rotary movement. If the called line isbusy at this time, ground potential will be present on the test contact69.

As a result, before relay 18 has had time to deenergize, busy relay 17will be ener ed over the circuit including wiper 66', contacts 59,contacts 55 and contacts 63.' Relay 17, in operating, closes a lockingcircuit for itself at contacts 48 and prepares the busy tone circuit atcontacts 46 in the usual manner, the latter circuit being closed as soonas relay 18 releases its arinatures at the cessation of the impulses ofthe second digit by the closure of contacts 53. The attendant will hearthe busy tone in her receiver, indicating to her that the calledsubscriber is busy, so

whereupon she will inform the calling main exchange subscriber of thisfact and then release the connection as will be described subsequently.

It will be assumed, however, that the called subscriber is idle at thistime, in which case no ground potential is present on the test contact69, and relay 17 is not operated. Instead, when relay 18 releases itsarmature at the cessation of this last-series of impulses, the switchingrelay 19 will be operated over its upper winding in the usual manner,the circuit thereof extending from ground on the release conductor 7,contacts 47, upper winding of relay 19, contacts 54, contacts 59, wiper66, bank contact 69, to battery through the winding of the switchingrelay of the lineswitchLS in the usual manner. Switching relay 19energizes and closes points in the talking circuit at contacts 57 and'62, closes a locking circuit for itself over its lower winding atcontacts '60, grounds the test contact 69 by the closure of contacts 58,and opens a point in the rotary magnet circuit at contacts 61. Theclosure of contacts 57 and 62 also completes the ringing circuit whichextends from the conductor 99' to which direct ground and a groundedringing generator are alternately connected, over the lower talkingconductor, through the ringer at'substation A, over the upper talkingconductor, and through the upper Winding of the ring cut-off relay 16 tobattery. The-attendant will hear the ring back tone in the usual manner,indicating to her that the called subscribers line is idle and thatthecalled subscribed is being signalled. a

It is unnecessary for the attendant to wait on the line until the calledsubscriber answers. She may choose, therefore, to disconnect hertelephone set from this connection so that she may give attention toother calls. To do this she merely replaces the responding lamps of allother busy trunk lines is extinguished. Thus the unnecessary burning ofthe busy lamps whenthe receiver on its switchhook is prevented. Itshould be noted that the indication given by the busy lamps such as if,is necessary only when the attendant wishes to select an idle trunk tomake a call, in which case she will remove her receiver, thereby closethe circuit of the busy lamps of all busy trunks. These operations willbe described more in detail subsequently.

lloth relays 20 i and 313 also deenergize when the attendant replacesher receiverl The separation of contacts 223 and 228 of relay 20adisconnects the attendants telephone set from in bridge of theconductors 252 and i, and by the closure of contacts 229 the bridgeincluding the lower winding of relay 206 is substituted therefore. Byreason oi this bridge including the lower winding oi relay 206 theconnector (3 is held in operated position. By the separation of contacts226 the circuit of the upper Winding of relay 206 is opened, but relay206 is held energized over its lower winding in series with the linerelay ll of the connector *6. By the separation of contacts 222 and 230the bridge including the retard coil 312 across the trunk conductors 202and 204 is opened, and by the closure of contact 231 another bridgeincluding relay 207 and contacts 216 and 239 and also relay 201 (itbeing noted that relay 201i was also in the bridge including the retardcoil 312) is substituted therefore. Re lay 201 remains energized andincidentally relay 207 energizes. By the separation of contact 225, theinitial holding circuit of relay 202 is opened. lFtelay 208, however, isheld over the circuit including conductor 253 and resistance llpreviously traced.

Relay 313, in deenergizing, again closes contacts 310 thereby making itpossible for the attendant to associate her telephone set with any othertrunk line by operating the corresponding key similar to key K. At thepresent time, with the receiver on its switchhook, only lamp l islighted which indicates that the called private automatic ex changesubscriber is being signalled but has not yet answered.

-l l hen the called subscriber answers the call by removing hisreceiver, the ring cut-oft relay 16 in connector C operates in the usualmanner and closes a locking circuit for itself over its lower winding atcontacts ac and disconnects itself and the ringing generator from thetalking conductors and completes the talking connection by closingcontacts 43 and a l. This operation also completes the circuit for theback bridge relay 14, through the windings o-fwhich talking battery isfurnished tor the called substation. Relay 14: energizes and byseparating contacts 33 disconnects ground potential from the discriminating conductor 6. The removal of ground commence conversation withthe subscriber at the main automatic exchange, the talking circuitextending over the heavy talking conductors including conductors 5 and8, conductors 252 and 254, condensers 262 and 26st, and the trunkconductors 202 and 204 extending to the main automatic exchange.

[it the termination of the conversation both subscribers will replacetheir receivers on their respective switch hooks. The replacement of thereceiver at the called subscribers substation opens the circuit of theback bridge relay 14 of the connector C. This relay thereupondeenergizes and again connects ground to the discriminating conductor 6by the closure of contacts 33. Since relay 208 is now deenergized andresistance R2 is shortcircuited by contacts 242, the placing of groundon conductor 253 causes both lamps L and L to light, and also causesrelay 314 to operate. The lighting of these lamps at this time indicatesto the attendant that the conversation has terminated and that thecalled subscriber has replaced his receiver. If the key K be operated tothe right, the buzzer 13 also sounds, giving further indication that acall has terminated (or that another call is awaiting attention).

It is also possible for the called subscriber to flash the attendant,should he wish to speak with her, by jiggling his switchhook in theusual manner. This operation causes relay 14 to energize and deenergizein quick succession causing lamps L and L to flash. lln response to thissignal the attendant may reconnect her telephone set across the tiunkline by again removing her receiver and momentarily operating the key Kto the left, causing the operation of: relay 20 i which conmeets hertelephone set across the line conductors 252 and 25 i as previouslydescribed.

To release the connection after the called subscriber has replaced hisreceiver as indicated by the lighted condition of lamps L and L theoperator merely operates the key K momentarily to the right. This closesa circuit momentarily for relay 205. Relay 205, in energizing, opens thebridge including the lower Winding of relay 206 by separating contacts234. The opening of this bridge causes the release of the line relay 11of the connector C whereupon the connector C re stores to normal in theusual manner. Relay 206 likewise deenergizes and-opens the bridge acrossthe trunk conductors 202 and 204 by separating contacts 239. The openingof this bridge permits the connector C in the main automatic exchange torelease in the usual manner (the other switches of the main automaticexchange having released responsive 6 to the replacement of the receiverby the calling subscriber). Rela 207 and relay 201 likewise deenergized.elay 201, in deenergizing, opens the circuit of relay 202, which alsodeenergizes and opens the circuit of re- 10 lay 203. By the restorationof these relays and relay 207 all the relays of the trunk relay groupTRG are restored to normal. By the separation of contacts 212 and 240the trunk line is again marked idle and ready for use in the extensionof another connection either to or from the main automatic exchange. Theseparation of contacts 215 opens a point in the circuit of lamp L solamp will remain dark upon a removal of the attendants receiver, thusindicating that this trunk is idle.

As previously stated, the private automatic exchange subscribers whoseservice is restricted to the establishment of connections with any ofthe other local subscribers of the private automatic exchange, cannotcomplete connections to the main automatic exchange or call theattendant. The other subscribers, however, whose service is notrestricted, may extend connection directly, to the main automaticexchange by dialing first a special digit such as the digit 0 and thendialing the regular directory number of the main automatic exchangesubscriber, or these subscribers may first call the attendant and tellher the name or the number of the subscriber with whom they wish tospeak, who in turn will set up a so-called tail-to-ta-il connection,obtaining connection first with the wanted main automatic exchangesubscriber and then recalling the calling private automatic exchangesubscriber. To describe these operations, it will first be assumed thata private automatic exchange subscriber such as the subscriber atsubstation A wishes to establish a connection with a subscriber at themain automatic exchange himself without the aid of the attendant: To doso he will remove his receiver and dial the digit 0 after which he willdial the regular directory number of the called main automatic exchangesubscriber.

Responsive to the removal of the receiver at the substation A thelineswitch LS operates in the usual manner and extends the connection toan idle connector such as the connector C, for example. When theconnection is extended to the connector C, line relay 11 operates andcloses a circuit for the release relay 12, which in turn operates andconnects ground potential to the release trunk conductor 7 andpreparesthe impulsing circuit in the usual manner. Responsive to thedialing of the digit 0, vertical magnet operates in series with relay.13 and steps the switch wipers opposite the tenth level bank contacts inwhich access is had to'the outgoing branches of trunks extending to themain automatic exchange. The connector C is provided with shaft springs91 and 92 which close when the shaft is raised opposite the ninth ortenth level of bank contacts. The closure springs 92 close the circuitfor relay 15 in series with the upper winding of relay 16. As a resultboth relays 15 and 16 ener 'ze. Relay 16 locks itself over its lower wining to the release conductor by the closure of contacts 40, opens theringing circuit by separating contacts 42 and-45, and closes points inthe talking circuit by closing contacts 43 and 44. Relay 15 operates andconnects the upper andlower windings of back bridgerelay 14 independentof the exchange battery by separating contacts 36 and 38 and closingcontacts 37 and 39. By the closure of contacts 34, before relay 13 hashad time to restore, a circuit is closed extending from ground appliedto the discriminating conductor 6 by way of the jumper 11 at thelineswitch LS, via springs 91, ofi-normal springs 94 (springs 94 openand springs 93 close whenever the switch wipers are rotated oil of thetenth set of contacts in the ninth or tenth level), contacts 31,contacts 63, through the windings of relay 17 to battery. Relay 17operates and closes a locking circuit for itself to the releaseconductor at contacts 48.

Shortly after the cessation of the impulses of this first digit, relay13 deenergizes and by closing its contacts 32 a circuit is closed forthe rotary magnet 21 which extends from ground by way of discriminatingconductor 6, contacts 35, springs 91, contacts 94, contacts 32, contacts49, contacts 61, through the winding of rotary magnet 21 to battery,relay 18 also operating in parallel therewith. The rotary magnetthereupon operates and moves the switch wipers into engagement with thefirst set of contacts in the tenth level, and opens the circuit of relay17 by separating contacts 63. Relay 17 thereupon deenergizes and opensthe circuit of the rotary magnet 21 by separating contacts 49 therebypermitting ma et 21 to deenergize and again close contacts 63. If thefirst trunk accessible in the tenth set of bank contacts is busy, groundpotential will be present on the test contact with which wiper 66 is inengagement. As a result relay 17 again operates before relay 18 has hadtime to deenergize over the circu'it which includes wiper 66, contacts59, contacts 55, and contacts 63. In energizing, relay 17 again closesthe circuit for rotary magnet 21 at contacts 49. Rotary magnet 21 willagain operate and rotate the swltch wipers into engagement with the nextset of bank contacts. In this manner the switch wipers will besuccessively rotated until they are brought into engagement with thebank contacts terminating an idle trunk, which will be assumed is thetrunk comprising conductors 202', 203, and 204. In this case no till are

hit

till

amazes ground potential will be present on the test contact 89 engagedby wiper 66 and conse quently relay it will not be reenergized. lnstead,switching relay 19 will be energized over its upper winding after relay18 deenergiues from ground on the release trunk conductor 7 over acircuit including contacts ll", the upper winding of relay 19, contacts54, contacts 59, wiper 66, test contact 89, to battery through theresistance ll". Relay 19 operates and performs circuit changes aspreviously described and extends the connection to the trunk conductors202 and 204.

As a result of the extension of the connectionto the trunk conductors202- and 204: a-

circuit is closed for the line rela of the lineswitch at the mainautomatic exc iange terminating the inter-exchange trunk comprisingconductors 202 and 204: in series with relay 201. This circuit extendsfrom ground by way of contacts 221, conductor 204, over the bridgeincluding the windings of back-bridge relay 1a (its upper and lowerwindings now being connected at contacts 37 and 39) over conductor 202through the winding of relay 201, trunk conductor 202, through thewinding of the line relay of the lineswitch lLS- to battery. in thiscircuit relay 201 operates and closes a circuit "for relay 202. Relay202 operates and opens the A. 0. bridge including the ringing relay 209normally across the trunk conductors at contacts 214i and closes a pointin the circuit of lamp L at contacts 215. New whenever the attendantremoves her receiver the lamp T1 will light indicating that this trunkis busy. lttelay 202, in operating, also prepares a circuit for relay203 at contacts 213.

The energization oi the line relay of the lineswitch LS at the mainautomatic exchange over the above traced circuit initiates the operationof this lineswitch to select a trunk to an idle selector such as theselector hi As soon as the lineswitch LS has selected an idle selectorand extended the connection thereto, the circuit for relay 203 at theprivate automatic exchange is closed by reason oi ground through thelower winding of the line relay ot the selector S it should be notedthat there is no ground connection normally connected to the lowerconductor an at the lineswitch LS When the latter circuit is closed,relay 203 operates and closes a locking circuit for itself at contacts218 and at contacts 220 connects conductor 204' with the trunk conductori thereby completing the extension of the talking connection to theselector S at the main automatic exchange.

All the foregoing operations described alter the connector t) was seizedhave taken place responsive to the first digit dialled by the callingsubscriber. Responsive to the dialing of the remaining digits otthecalled number, the selector S and other selectors and a connector aresuccessively operated in ing each series of impulses and b the usualmanner to extend the connection to the called subscriber, the connectorC operating as a repeater to repeat the impulses over the inter-exchangetrunk. In this case the relay 18 of the connector C also operatesdurclosing contacts 52 disconnects the bridge lncluding the baclebridgerelay 14 and places a direct bridge across the conductors 202' and 204.This bridge is intermittently opened and closed responsive to the digitsdialled by the operation of line relay 11 at contacts 26.

When the called main exchange subscriber answers the call by removinghis receiver he may commence conversation with the private automaticexchange subscriber. When the conversation is terminated bothsubscribers will replace their receivers. The replacement of thereceiver at the private automatic exchange substation opens the circuitof line relay 11 which in turn deenergizes and opens the circuit ofrelease relay 12. Release relay 12 removes ground from the release trunkconductor 7 and by closing contacts 28 closes a circuit for releasemagnet which in turn energizes and restores the connector O to normal.The removal of ground from release conductor 7 also opens the lockingcircuits "for relay l6 and relay 19, causing these relays to deenergizeand open the bridge across the conductors 202' and 204. The removal ofthe bridge across these conductors causes the release of the switches inthe automatic exchange in the usual manner, and also opens the circuitof relay 201. Relay 201 deenergizes and opens the circuit of a relay202, which in turn deenergizes and opens a point in the circuit oflamp Lat contacts 215.

Relay 202, in deenergizing, also opens the holding circuit for relay 203at contacts 213, and removes ground from the conductor 203 at contacts212, thereby again placing this trunk in idle condition.

its previously stated a private automatic exchange subscriber (havingunrestricted service) instead of setting up the connection himself, maycall the attendant and request her to set up the connection to the mainautomatic exchange for him. The operations performed to call theattendant, and the manner in which the attendant setsup a connection tothe main automatic exchange and then recalls the private automaticexchange subscriber will now be described. For this purpose it will beassumed that the subscriber at substation A again wishes to speak withsome main automatic exchange subscriber and chooses this latter courseto obtain connection. To call the attendant, the subscriberatsubstantion A removes his receiver and in this case dials the digit 9.Responsive to the removal of the receiver the lineswitch LS againoperates in the usual manner to select a trunk to an idle connector suchas the connector C, for example. Responsive to the lllll lllt ' dialingof the digit 9, the connector 0 open ates to elevate its wipers oppositethe ninth level of bank contacts, and then selects an idle one of thetrunks accessible therein. These operations all take place insubstantially the same manner as described above when the connector Cwas operated to select a trunk to the main automatic exchange, it beingnoted that the shaft springs 91 and 92 close as the shaft is raisedeither to the ninth or to the tenth level. I v

It may be assumed that the trunk line comprising conductors 301, 302,and 303 is the one selected, relay 19 operating initially over its upperwinding over conductor 303 in series with lamp L and relay 314. Lamp L"lights and again the buzzer B sounds (providing the key K is operated tothe right). The lighting of the lamp L indicates to the attendant that a.call has been extended to her, whereupon she will operate the key K assoon as she is ready to take care of the call. To answer the call, theattendant will remove her receiver from the switchhook and operate thekey K This closes a circuit which extends from ground at the switch hooksprings 399, thecontacts 310, springs of key K through the upper windingof relay 300 to battery. Relay 300 operates and closes a locking circuitfor itself through its lower winding in series with relay 313. Relay 313operates and by separating contacts 310 opens the initial energizingcircuit of relay 300 and also prevents the operator from I associatingher telephone set with any other trunk at this time. Relay 300, inoperating, also places direct ground potential on the release conductor303 at contacts 306, and by separating contacts 307 opens the circuit ofthe lamp L. By the closure of contacts 308 and 309, attendants telephoneset is bridged across the talking conductors 301- and 302. Current forthe attendants telephone set is fed through I impedance coil 331 bridgedacross trunk conductors 301 and 302.

The attendant may now converse with the.

station A wishes connection. After obta'intelephone set from the trunkover which she' was called. Replacing her receiver separates theswitchhook springs 399 thereby opening the circuit of relay 300 andrelay 313. These relays then deenergize and restore to normal.

To complete the call to the wanted main automatic exchange subscriber,the attendant again removes her receiver and she momentarily operatesthe trunk key of an idle trunk to the left (the idle conditionof anytrunk being indicated by the non-lighted condition of the lampcorresponding to lamp L after the attendant has removed her receiver).It will be assumed that the trunk line comprising conductors 202 and 204is idle at this time and is the one chosen. Operating the key K to theleft momentarily, the receiver being removed, causes the operation ofrelay 204 individual to the trunk line. Relay 204 operates and performscircuit changes as previously described, including the closing of alocking circuit for itself in series with relay 313, the placing of theretard coil 312 in series with the relay 201 across the outgoing trunkconductors 202 and 204. The closing of the circuit for relay 206 whichrelay operates. with the same result as previously described and inconjunction with relay 204 laces the attendants telephone set includinger dial across the trunk conductors 252 and 254. The placing of theoperators telephone set including the dial across the trunk conductors252 and 254, initiates the operation of the lineswitch LS which inoperating selects an idle connector, but this operation at this time isonly incidental as will be shown presently.

After operating the key K momentarily to the left, the attendantoperates the common dialing key K to the left and then dials the numberof the called main automatic exchange subscriber. Throwin the key K tothe left disconnects the attendants telephone set including the dialfrom in bridge of the conductors 252 and 254 by tacts 321 and 322, anddisconnects the retard coil 312 from in bridge of the trunk conductorsto the main automatic exchange by separating contacts 323 and 324 andsubstitutes the operators telephone set including the dial therefore byclosing contacts 325 and 326. The disconnection of the operatorstelephone set from in bridge of the conseparating con-' ductors 351 and352 allows line-switch LS to restore to normal, its wipers, however,remaining on the bank contacts last selected.

Operatin key K to the left, by closing contacts 32 closes a circuitwhich extends from ground at contacts 221, over contacts 228', contacts327, contacts 325, through the operators telephone set, contacts 326,conductor 361, contacts 222, through the winding of relay 201, trunkconductor 202, through the winding of the line relay of line switch LSat the main automatic exchange. Both the line relay of the .line switchLS and relay 201 energize. Relay 202 energizes as a result of relay 201energizing, performing the same operations as described previously,including the lighting of the lamp L by the closure contacts 215 and thepreparation of the circuit of relay 203 at contacts 213. The line relayof the line switch LS, in operating, causes the line switch to operateand extend the connection to an idle selector such as the selector S forexample. Relay 203 then op crates in series with the lower winding ofthe line relay of selector S with the results previously described.

The operators dial is now included in the bridge across the outgoingtrunk conductors 202 and 204 to the main automatic exchange, andautomatic switches at the mainautomatic exchange respond successively tothe diglts dialled by the attendant and extend the connection to thecalled subscriber in the usual manner. When the called subscriberanswers, the attendant may converse with him and inform him that aparticular party at the private automatic exchange desires to speak withhim, whom she will call while he, the called main exchange subscriber,keeps his receiver to his ear.

The attendant now throws the key K to the right thereby again placingthe retard coil 812 in bridge of the outgoing trunk conductors and againplacing her telephone set in bridge of the trunk conductors 252 and 254.Again the lineswitch LS operates to extend the connection to an idleconnector such as the connector C, for example. It is noted thatthrowing of the key K to the right merely opens the talking circuit tothe main automatic exchange in order to prevent the called subscriberfrom hearing disagreeable noises which would be produced by theattendants operating the dial to set up the connection to the privateautomatic exchange subscriber. The attendant now dials the number of thesubstation A causing the connector C to operate as previously describedand extend a connection to the substation A. The attendant, aftercompleting the dialing of the number of the substation A and hearing theusual ring back tone which assures her that the substation A has notbecome busy in the meantime, may release her telephone set from thistrunk as described in the previous connection. She is also informed whenthe calling subscriber at A removes his receiver by the extinguishing oflamp L and is likewise informed when he replaces his receiver by therelighting of lamps L and L The attendant when so notified releases theconnection by throwing the key K to the left momentarily, thisinitiating the release operation as previously described.

lit remains to be mentioned, that the subscribers at the privateautomatic exchange who are restricted to service within the prirateautomatic exchange and are not allowed to extend connections to the mainautomatic ernhange and could not extend connections thereto even thoughthey attempted to do so. The manner in which this restriction is given.does not concern the invention. However,

I the manner illustrated in the drawings may briefly be described. Aspreviously mentioncd, to restrict the service of the subscriber atsubstation A, for example, it is merely necessary to remove the jumper11 connecting the contacts 9 and 10. If now the subscriber atsubstationA, after the jumper 11 has been removed, attempts to extend a connectionto the main automatic exchan e by dialing the digit (or attemptsto otain connection with the attendant by dialing the digit 9), theconnector 0 will again operate and raise its wipers opposite the tenth(or ninth) level. In this case there will be no ground potential presenton the conductor 6, but relay 17 will again operate when springs 91 areclosed bythe elevation of the shaft to the tenth (or ninth) level, thistime in series with the resistance R (before series relay 13 has hadtime to deenergize). However, magnet 21 is insufficiently energizedthrough the resistance R (after relay 13 falls back) to operate androtate the switch wipers into engagement in the first set of contacts inthe level opposite which the wipers have been positioned. Therefore noconnection is established, but the relay 17 remains energized and thesubscriber who attempted connection receives the busy tone.

This completes the description of the invention. What is thought to benew and is desired to have protected by Letters Patent is specificallypointed out in the appended claims.

What is claimed is:

1. In a telephone system, trunk lines, a key and a relay for each trunkline, operating circuits for said relays including said keys and acommon conductor, a telephone set, means responsive to a momentaryactuation of any one of said keys for operating a relay to associatesaidtelephone set with the corresponding trunk line, and means foropening said common conductor to prevent the association of saidtelephone set with any other trunk line by the subsequent operation ofany other key.

2. In a telephone system, trunk lines, a key for each trunk line, atelephone set including a switchhook, means responsive to the operationof said switchhook and a momentary actuation of any one of said keys forassociating said telephone set with the corresponding trunk line, andmeans for preventing the association of said telephone set with anyother trunk line by any subsequent operation of any other key until theswitchhook has been restored and again operated.

3. In a telephone system, a trunk line having an incoming and anoutgoing branch, a key, a telephone set, means separate from said keybut automatically responsive to a momentary actuation thereof forconnecting said telephone set across the conductors of said incomingbranch and for connecting a bridge across the conductors of saidoutgoing branch.

4. In a telephone system, a trunk line having an incoming and anoutgoing branch, a key, a telephone set, means automat cally r esponsiveto a momentary actuation of said key for connecting said telephone setacross the conductors of said incoming branch and for connecting abridge across the conductors of said outgoing branch, and a key fordisconnecting said telephone set from sald 1ncoming branch and forsubstituting said telephone set for said bridge.

5. In a telephone system, a trunk km, a calling device, a key, meansresponslve to a momentary operation of said key for associating saidcalling device with said trunk line means thereafter controlled by saidcalling device for extending a connection over said trunk line to acalled telephone line, means controlled at will for disassociating saiddialfrom said trunk line, and means controlled at will for releasingsaid connection and for also disassociating said calling device fromsaid trunk line in case it is still associated therewith when saidreleasing means is operated.

6. In a telephone system, a connector accessible to two kinds of lines,a conductor in said connector, means in said connector for causing it toexecute an automatic rotary mo-' tion controlled over said conductorwhen said connector is taken into use over one kind of line, and asignal controlled over said cona o 'ductor when said connector is takenlnto use 0nd line, an automatic switch accessible to said lines, asignal for said first line, means for said second line for-placing apotential on a conductor of said connector to initiate an operation ofsaid connector when said connector is taken into use over said secondline, and means in said connector for placing a potential on saidconductor to operate said signal when said connector is taken into useover said first line.

8. In a telephone system, trunk lines, a key for each trunk line, a.telephone set, means responsive to a momentary actuation of any one ofsaid keys for associating said telephone set with the correspondingtrunk line, means for then locking said telephone set to thecorresponding trunk line independent of the key, and means common to allof said trunk lines for disabling said locking means. i

9. In a telephone system, trunk lines, a key for each trunk line, atelephone set, switch hook springs for said set, means responsive to amomentary actuation of any one of said keys with said springs operatedor associating said telephone set with t e corresponding trunk line, andmeans effective only as long as the switchhook springs remain operatedfor locking said tele hone set to the corresponding trunk line inependent of the key. p

10. In a telephone system, trunk lines, a relay for each trunk line, akey for each trunk line, a telephone set, means responsive to themomentary operation of any one of said keys for operating thecorresponding one of said relays for associating said telephone set withthe corresponding trunk line, means for maintaining the operated relayoperated independent of the key,- and a com mon relay controlled by saidmeans for opening the circuits of all of said first relays to preventthe operation of any other relay after one is operated.

11. In a telephone system, trunk lines, a trunk relay for each trunkline, an automatic switch terminating each trunk line, a telephone set,means for actuating any one of said relays, means controlled by theactuated relay for associating said telephone set with the correspondingtrunk line and for initiating the operation of the switch terminatingthe corresponding trunk line, and a common relay actuated in series withthe particular one of said trunk relays actuated for preventing theactuation of any other trunk relay thereafter.

12. In a telephone system, trunk lines, a

trunk relay for each trunk line,.a key for telephone set with thecorresponding trunk line, a common relay actuated in series with theparticular one of said trunk relays actuated for preventing theactuation of any other trunk relay thereafter, and separate means fordeactuating the actuated trunk relay and the common relay.

13. In a telephone system, trunk lines,'each comprising two inductivelycoupledsections, a calling device, means for associating said callingdevice with one section of any of said trunk lines, and a key common tosaid trunk lines for disassociating said calling device from said onesection and associating it with the other section of the same trunkline.

14. In a telephone system, a trunk line extending from a main exchangeto a branch exchange, a branch for said trunk line at the branchexchange normally disconnected from the trunk line, a key, and meansresponsive to a momentary actuation of said key for inductivelyconnecting said branch with said trunk line.

15. In a telephone system, trunk lines, a normally disconnected branchfor each trunk line, a first and a second set of talking leadsinductively coupled, a key individual to each trunk line, meansresponsive to the momentary actuation of any key for-connecting the lidfirst set of talking leads to the corresponding trunk line and thesecond set of talking leads to the corresponding branch.

16. in a telephone system, trunk lines, a normally disconnected branchfor each trunk line,- a first and a second set of talking leadsinductively coupled, a key individual to each trunk line, meansresponsive to the momentary actuation of any key for connecting thefirst set of talking leads to the corresponding trunk line and thesecond set of talking leads to the corresponding branch, separateinductive coupling means for each trunk, and means tor substituting theseparate coupling means of the corresponding trunk for the first and thesecond set of inductively coupled talking leads.

17. In a telephone system, trunk lines, a branch for each of said trunklines, a key for each of said trunk lines, a common link, and meansautomatically responsive to the momentary operation of the key of any ofsaid trunk lines for inductively coupling the corresponding trunk linewith its branch via said common link.

18. in a telephone system, a subscribers station, a trunk linecomprising two talking conductors and a third conductor, means includingan automatic switch for extending a connection from said trunk line tosaid subscribers station, means in said switch for connecting groundpotential to said third conductor when a connection to said station isextended, for disconnecting the same from said third conductor when thesubscriber at the station answers the call, and for reconnecting thesame to said third conductor when the call is terminated, a first signaloperated by the initial connection of ground potential to said thirdconductor, and a second signal operated by the second connection ofground potential to said third conductor.

19. in a telephone system, trunk lines connecting two exchanges, anattendants cabinet at one of said exchanges, a telephone set. keys andsupervisory lamps in said cabinet, and relays remote from said cabinetand associated with said trunk lines for controlling said lamps and forconnecting said telephone set with any of said trunk lines under thecontrol of said keys.

20. in a telephone system, a t 'unk line, an automatic switch, means toroperating said switch to seize said trunk line, an attendants cabinet, asignal at said cabinet, and a relay in said switch energized in serieswith said signal when said trunk is seized by said switch. r

21. in a telephone system, a trunk line comprising two talking"conductors and a third conductor, an automatic switch, means foroperating said switch to seize said trunk line, an attendants cabinet, asignal at said cabinet, and arelay in said switch energized over saidthird conductor in series with said signal when said trunk is seized bysaid switch.

22. In a telephone system, an attendants switchboard, an automaticswitch, a trunk line passing through said switchboard and terminating insaid switch, an attendants telephone set, means for connecting saidtelephone set with said trunk line to answer calls thereover, andcircuit arrangements for supplying current for the transmitter of saidtelephone set from said switch.

23. In a telephone system, a trunk, an automatic switch terminating saidtrunk, means for seizing said trunk, other lines accessible to saidswitch, means for causing said switch to hunt an idle line responsive tothe seizure of said trunk, a relay for said trunk operated in serieswith one conductor of said trunk, a second relay for said trunk, meanscontrolled by said first relay for connecting said second relay to theother conductor of said trunk, and means for operating said second relaywhen said switch finds an idle line.

24. In a telephone system, a trunk, an automatic switch terminating saidtrunk, means for seizing said trunk, other lines accessible to saidswitch,means for causing said switch to hunt an idle line responsive tothe seizure of said trunk, a relay for said trunk operated in serieswith one conductor of said trunk, a second relay for said trunk, meanscontrolled by said first relay for connecting said second relay to theother conductor of said trunk, means for operating said second relaywhen said switch finds an idle line, and means controlled by said secondrelay for disconnecting said second relay from the other conductor ofsaid trunk after it is operated.

25. In a telephone system, a trunk line, an automatic switch terminatingsaid trunk line, means for seizing said trunk, said trunk linecomprising two conductors, one of which is continuous from the point ofseizure to said switch and the other of which has a normally open pointbetween the point of seizure and the automatic switch, means foroperating said switch, and means for closing the normally open point inthe said other conductor of said trunk line after said switch has beenoperated.

26. In a telephone system, a trunk line, an automatic switch terminatingsaid trunk line, means for seizing said trunk line, said trunk linecomprising two conductors, one of which is continuous from the point ofseizure to said switch and the other of which comprises two normallydisconnected sections, means controlled over the first section of saidother conductor in series with said continuous conductor for operatingsaid switch, and means controlled over the second section of said otherconductor for connecting said sections after said switch has beenoperated.

27. In a telephone system, a trunk line, an automatic switch terminatingsaid trunk line,

a line relay for said switch, means for seizing said trunk line, asecond relay operated over one conductor of said trunk line in serieswith said line relay when said trunk is seized, means for operating saidswitch, athird relay for said trunk line, circuit arrangementscontrolled by said second relay for operating said third relay over theother conductor of said trunk line after said switch has-been operated,and means controlled by said third relay for completing a talkingcircuit over said trunk line.

28. In a telephone system, trunk lines, a key for each trunk line, atelephone set in.- cluding a receiver, means responsive to the removalof the receiver and the operation of any one of said keys forassociating said telephone set with the corresponding trunk line, meansfor preventing the association of said telephone set with any othertrunk line by the subsequent operation of any other key, and meanscontrolled by the replacement of the receiver for disabling saidpreventing means.

29. In a telephone system, an automatic switch, a trunk line terminatingin said switch, means controlled, over a conductor of said trunk lineunder certain conditions for causing said switch to operate in adistinctive manner, a signal, and means in said switch effective undercertain other conditions for controlling said signal over saidconductor.

30. In a telephone system, a line, a signal for said line, a switch andmeans for operating it to connect with said line to extend a call, arelayin said switch operated in series with said signal responsive tothe connection of said switch with said line, and means responsive tothe answering of the call for disabling said signal.

31. In a telephone system, a trunk comprising two talking conductors anda third conductor, a signal normally connected to said third conductor,a switch and means for operating it to seize said trunk to extend aconnection, a relay in said switch operated in series with said signalresponsive to the seizure of said trunk, and means responsive to theanswering of the call for disconnecting said signal from said thirdconductor.

32. In a telephone system, a trunk line andmeans for seizing it toextend a connection, a relay and a resistance normally bridged acrossthe conductors of said trunk line,

means for operating said relay responsive to the seizure of said trunkline to mark said trunk line busy, means responsive to the answering ofthe call for opening said bridge, and means for placing said relay inbridgeof said conductors independent of said resistance to maintain theconnection.

33. In a telephone system, an attendants position, a trunk lineextending through said position, means for extending a call via saidtrunk line to said position, a signal operated responsive to theextension of a call, means for disabling said signal responsive to theattendant answering the call, means controlled by the attendant forfurther extending the call to a called station, a second signaloperative responsive to the further extension of the call, means fordisablingsaid second signal responsive tothe answering of the call, andmeans for reoperating said first and said second signals responsive tothe termination of the call. I

34. In a telephone system, an attendants position, means for extending acall to said position, a signal at the position operated responsive to acall being extended and disabled responsive to the attendant answeringthe call, means controlled by the attendant for further extending a callto a wanted station, a second signal at the position operated responsiveto the further extension of the call and disabled responsive to the callbeing answered at the wanted station, and

means for reoperating said first signal and said second signalresponsive to the call being terminated at the wanted station.

35. In a telephone system, a telephone set including a switch hook, aplurality of trunks of two different classes, a key for each of saidtrunks, means eflective when the switchhook is actuated and responsiveto the momentary actuation of one of said keys for associating thecorresponding trunk .with said telephone set, means responsive to thedeactuation of the switchhook for disassociating the connected trunk andthe telephone set providing the connected trunk is of one class, andmeans responsive only to the fur ther actuation of the key fordisassociating the connected trunk and the telephone set plroviding theconnected trunk is of the other 0 ass.

36. In a telephone system, a trunk com prising three normallydisconnected sections, a relay energized responsive to a call over saidtrunk for connecting the first and second sections of the trunk, asecond relay having two windings, means for operating said second relayover one of said windings responsive to the operation of said firstrelay, means for connecting the second and third sections of the trunkresponsive to the operation of said second relay, means for deenergizingsaid first relay, and means for completing a holding circuit for saidsecond relay including the other winding of said second relay bridgedacross the conductors of said trunk responsive to the deenergization ofsaid first relay.

, 37. In a telephone system a main office, a branch ofiice comprising anautomatic exchange, main lines connecting the main oflice with thebranch oflice and terminating in the automatic exchange, subscriberstelephone lines terminating in the automatic exchange, subscribersstations having telephone appaith ratus associated with said subscriberslines, one of said subscribers apparatus being pro- "vided with meansfor mediating the incoming trafic from the main oiiice comprisingswitching means at the automatic exchange for connecting the telephoneline of the mediating subscribers apparatus with each of said mainlines, circuits for said switching means, keys on the mediatingapparatus for operating said switching means over said circuits, andcall indicating means on the mediating apparatus for indicating callsfrom the main ofice.

38. In a telephone system a main oflice, a branch oflice comprising anautomatic exchange, main lines connecting the main oiiice with thebranch oifice and terminating in the automatic exchange, subscriberstelephone lines terminating in the automatic exchange, subscrihersstations having telephone apparatus associated with said subscriberslines, one of said subscribers apparatus being provided with means formediating the incoming traflic from the main ofice comprising switchingmeans at the automatic exchange for connectin the telephone line of themediating subscri ers apparatus with each of said main lines, circuitsfor said switching means, keys on the mediating apparatus for operatingsaid switching means over said circuits, call indicating means on themediating apparatus, and means for connecting a main line with asubscribers line through the automatic exchange under the control of themediating apparatus.

in witness whereof, hereunto subscribe my name this 4th day of April, A.D. 1927.

THUS. F. CROCKER.

